Distributed temperature sensing (DTS) is a state-of-the-art tool that possess an ability to monitor temperature rates over large territory and across wide temporal scales. This fiber optic technology has proved to be effective in different spheres and industries. However, despite the long field experience story, it still has its limitations and challenges apart from all the advantages. For example, when we talk about its application at shallow or deep depths.
The main difficulties in Distributed Temperature Sensing application
Despite all the progress that was achieved during this decade, distributed temperature sensing still meets some challenges. For example, when applied to the ocean, since dynamic oceanographic processes have a wide range of parameters, ranging from various types of turbulence to different climates, all data obtained from DTS systems fully help in understanding the dynamics of a complex ocean. However, different constraints can make modifications in time scales creating restrictions. Furthermore, there is a need for many additional advanced equipment for broad spatial resolution. That’s why it’s still complicated to use DTS in oceanography. However, now there are cases when distributed temperature sensing (DTS) is applied, for instance, in the Atlantic.
Recently, the scientists announced the first experiments on the seafloor of the Arctic sea ice with the help of the distributed acoustic sensing (DAS) system. This research has shown that fiber optic technology is effective, despite all the difficulties the scientists have faced due to the harsh environment. The system recorded a range of events that commonly applied equipment couldn’t even detect. Moreover, the DAS technology has detected the icequakes, various climate signals, and marine life.
From the other side, DTS systems can be applied in measuring surface water temperature spatial variability in lakes and rivers. The received data helps in the assessment of different factors such as estimating fish habitat and thermal inertia, the interaction between surface water and groundwater, etc. Usually, distributed temperature sensing is successfully applied in rivers and lakes with sensitive and high-resolution temperature monitoring under the wide temporal and spatial scales. Nevertheless, difficulties may arise in streams with cobbly or bedrock-lined streambeds. To avoid all the challenges, more expensive additional technologies are needed.
There are other factors that should be ensured like sensitive equipment needs protection and continuous power to work. Besides, optical fibers are delicate, they shouldn’t be bent or crimped.
How the Distributed sensing system works
Distributed sensing systems are appealing because they are able to continuously sample preserving while maintaining relatively high temporal and spatial resolution. Moreover, the accuracy indicators stay the same over a vast territory.
Distributed temperature sensors measurement allows to constantly observe temperature changes along the fiber optic cable. In this fiber optic technology the whole cable plays the role of the sensing element that measures temperature. It differs this method from the usual electrical temperature measurement. Moreover, the distributed temperature sensing is regarded as the most cost-effective and efficient system among the modern temperature measurement technologies.
The main operation principles of measurement are built on detecting the back-scattering of light:
- The first type is an optical fiber that uses Raman scattering. This approach was invented in the United Kingdom. Optical fibers are usually made from doped quartz glass. When the light falls on the excited molecular oscillations, the electrons of the molecule and the electrons of the molecule start interaction. This process is called Raman scattering and results in scattered light.
- The second method is the Brillouin scattering-based approach. It was mostly developed in the 1990s. It refers to the scattering of a light wave by an acoustic wave because of the interaction with the acoustic phonons. Thanks to the ability of the Brillouin scattering of making both frequency down- and up-shifted light, this method can be applied whether for distributed temperature or strain sensing. It can contain both, but they can’t work at the same time.
- The third technique is named Rayleigh back-scattering. This is the latest development. As well as for the previously developed distributed sensors, a usual optical fiber can be used as the sensor. It allows the entire cable to be used as a single sensor, without purchasing expensive individual sensors. Scientists applied this technique, for example, for measuring distributed temperature in a nuclear reactor.
If we compare all these three techniques, each of them has its pros and cons. According to the scientists, the Rayleigh scattering demonstrates the highest rates in comparison with other types. However, it has limits in a range of fiber length. This factor is crucial for long lengths of cables’ monitoring. For this characteristic, the Brillouin scattering shows the best results. Besides, it has temperature sensitivity and good measurement time. Moreover, Brillouin scattering allows to detect distributed strain, unlike the other two methods. But usually it is applied either for distributed temperature measurement or strain. According to the data, Brillouin scattering is more often used as a substitute for Raman scattering.
DTS systems in field experiments
In accordance with the final field experiments, despite all the challenges, temperature measurements with the help of the DTS systems have been performed successfully in various environments including rivers, lakes, seas, etc. The fiber Bragg grating sensors have been applied both in fresh and sea water and demonstrated good results. Furthermore, it refers to simultaneous measurement of temperature and depth which has been impossible for previous fiber sensors.
Modern fiber optic sensors provide the parallel measurements of temperature and pressure at the same place. Besides, in comparison with other methods, fiber optic technology provides much lower power consumption. It allows the DTS systems to work longer and makes longer experiments and observation possible.
The developed fiber optic technology can be used for measurements and monitoring of the physical parameters. Moreover, it is well-placed for many cases and can be applied to various applications, such as wave and tide gauges, tsunami warning systems, etc.
All in all, we can say that distributed temperature sensing (DTS) can be successfully applied in various cases at shallow depths due to their diversity. The system can be designed and installed in accordance with the existing conditions and parameters in every single case.
Optromix is a DTS system manufacturer that provides top of the line distributed temperature sensing systems suitable for monitoring commerce networks. If you have any questions or would like to buy a DTS system, please contact us at info@optromix.com